1. Field of the Invention
The present invention relates Liquid Crystal Display, and more particularly, to pixel element of Liquid Crystal Display.
2. Description of the Prior Art
The Liquid Crystal Display can be classified according to kinds of the liquid crystal, kinds of driving method, kinds of light source, and the like. One type of the Liquid Crystal Display—Optically Compensated Birefringence Liquid Crystal Display or Optically Compensated Bend Liquid Crystal Display, OCB LCD—has a quick response time so that it can provide fluent visions to the viewer.
Before normal operation, the liquid crystal molecules of the OCB LCD must be transformed from the splay state to the bend state. FIG. 1A and FIG. 1B respectively illustrate the splay state and bend state of the liquid crystal molecules of the OCB LCD, wherein FIG. 1A shows the splay state, and FIG. 1B shows the bend state.
As shown in FIGS. 1A and 1B, an OCB LCD 10 comprises a liquid crystal layer 11 arranged between a thin-film transistor substrate 13 and a color filter substrate 12. Before an electrical field is applied to the liquid crystal layer 11, the liquid crystal molecules of the liquid crystal layer 11 is arranged at splay state. When an electrical filed is applied to the liquid crystal layer 11, the liquid crystal molecules of the liquid crystal layer 11 are transformed to the bend state. This transformation process is typically called as “start up” procedure. The OCB LCD cannot be normally operated until the “start up” procedure is completed. A conventional OCB LCD typically needs several minutes for carrying out the start up procedure, and always the user is impatient to wait.
As shown in FIG. 2, U.S. Pat. No. 6,597,424 discloses a pixel element of an OCB LCD to speed the start up procedure. Data lines 21 and gate lines 22 define a pixel element, which comprises a pixel electrode 24 and a switch transistor 23 for driving the pixel electrode 24, where the pixel electrode 24 has recess portions 25a and protrusion portions 25b at the neighborhood of its edges, and the data lines 21 and gate lines 22 have corresponding protrusion portions 26a/27a and recess portions 26b/27b. Some potential differences are applied between the pixel electrode 24 and the data lines 21 and between the pixel electrode 24 and the gate lines 22, thereby forming a transverse electric field to generate bend seeds that can help the transformation of the state of the liquid crystal layers, so that the start up procedure can be accelerated.
Although the above pixel element can speed the start up procedure, the aperture ratio is inevitably decreased. Because the shape of the protrusion portions 25b/26a/27a and the recess portions 25a/26b/27b are irregular, it is needed to be covered by a black matrix having the same irregular shape but a more large area, and therefore the aperture ratio is decreased.
Therefore, it would be advantageous to provide a pixel element and a method for producing the pixel element, which the start up procedure can be speeded and an excellent aperture ratio can be maintained.